Lesion material from Treponema-associated Hoof Disease of wild elk induces disease pathology in the sheep Digital Dermatitis model

Authors: Wilson-Welder, Jennifer; Olsen, Steven; Alt, David; Bayles, Darrell; HAN, SUSAN - Colorado State University; MANSFIELD, KRISTIN - Washington Department Of Fish & Wildlife

Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2021
Publication Date: 1/12/2022
Citation: Wilson-Welder, J.H., Olsen, S.C., Alt, D.P., Bayles, D.O., Han, S., Mansfield, K. 2022. Lesion material from Treponema-associated Hoof Disease of wild elk induces disease pathology in the sheep Digital Dermatitis model. Frontiers in Veterinary Science. 8. Article 782149. https://doi.org/10.3389/fvets.2021.782149.
DOI: https://doi.org/10.3389/fvets.2021.782149

Interpretive Summary: A severe hoof disease is affecting wild free-roaming elk in the Pacific Northwest. As the disease progresses, affected animals become very lame, hooves can become disformed, overgrown, even completely sloughed, leaving the animals vulnerable to malnutrition, predation and early death. Spiral shaped bacteria in the Treponema genus have been found consistently with this hoof disease giving it the name Treponeme-Associated Hoof Disease. In order to show that it is an infectious bacterial disease, we took lesions from wild elk and used them in a model previously used to develop digital dermatitis lesions in sheep, a similar disease that affects livestock. By 4-weeks following inoculation with the elk lesion tissue, majority of the sheep developed the characteristic lesions. Further analysis showed several of the Treponema species associated with the hoof disease in the induced sheep lesions as well as other bacteria form the elk lesion material in the sheep lesions. Understanding that Treponeme-Associated Hoof Disease is a transmissible, infectious bacterial disease is the first step in developing diagnostics, therapeutics and making science-driven wild elk management decisions.

Technical Abstract: A disease among wild, free-roaming elk in the Pacific Northwest has been reported since 2009. Causing severe lesions at the hoof-skin junction, penetrating into the hoof structure leading to severe lameness, misshapen hooves, and in some cases sloughed hooves leaving the elk prone to infection, malnutrition and premature death. Isolated to the feet or hooves, this disease has been termed Treponeme-Associated Hoof Disease due to the numerous Treponema found within the lesions. Spread of the disease among herds suggested an infectious etiology. In order to determine that there was a transmissible infectious component to this elk hoof disease, elk lesion homogenate was used in a sheep induction model of digital dermatitis. 10 animals were inoculated with lesion material and lesions developed over 7 weeks. Majority of the inoculated feet developed moderate to severe lesions at the 2- or 4-week post-inoculation observation timepoints, with 16 of the 18 observed feet at 4-weeks having spirochetes associated with the lesions. Histopathology showed spirochetes at the invading edge of the lesions along with other hallmarks of the elk hoof disease, neutrophilic inflammatory infiltrate and keratinocyte erosion. Treponema specific PCR showed that 3 treponema phylotypes associated with elk hoof disease and digital dermatitis were present. Infected sheep showed an increase in anti-treponema IgG compared to negative control sheep and pre-exposure samples, indicating both naiveite prior to inoculation and some level of exposure to the Treponema in the developing lesions. Analysis of the bacterial microbiome by sequencing of the 16S rRNA gene showed a community structure in the resulting sheep lesions that was highly similar to that of the elk lesion homogenate used as the inoculum, with several bacterial taxa overrepresented in the infected samples as compared to the negative process control sheep samples. In conclusion, there is a highly transmissible, infectious bacterial component to elk Treponeme-Associated Hoof Disease which includes several species of Treponema as well as several other bacterial phyla.